Will Portlister plugin still be required with 1.8.0?
It's never been required? But if you want to use it then it will still do its job.
Actually I don't even know exactly what it does, I installed it as a hot fix recommended by Gina a while ago and wondered if it's function had either become unnecessary or was included in new releases?
Portlister automatically detects when devices are plugged in and refreshes the list, or I think there may be an auto connect option. Auto connecting/refreshing is not implemented, and I can't think of what issue it may have been fixing for you off the top of my head.
I'm not even sure it was fixing anything, I installed it because of an issue that Gina pointed out.
Yes, it's particularly handy when using power supply control, to automatically detect and connect to the printer after it powers up.